diff --git a/packages/studio/src/player/components/TimelineGroupHeader.test.tsx b/packages/studio/src/player/components/TimelineGroupHeader.test.tsx
new file mode 100644
index 000000000..41546eb37
--- /dev/null
+++ b/packages/studio/src/player/components/TimelineGroupHeader.test.tsx
@@ -0,0 +1,76 @@
+// @vitest-environment happy-dom
+
+import React, { act } from "react";
+import { createRoot } from "react-dom/client";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { TimelineGroupHeader } from "./TimelineGroupHeader";
+import { defaultTimelineTheme } from "./timelineTheme";
+
+(globalThis as unknown as { IS_REACT_ACT_ENVIRONMENT: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+function renderHeader(
+  overrides: Partial<React.ComponentProps<typeof TimelineGroupHeader>> = {},
+): HTMLElement {
+  const host = document.createElement("div");
+  document.body.append(host);
+  act(() => {
+    createRoot(host).render(
+      <TimelineGroupHeader
+        label="Voiceover"
+        memberCount={5}
+        isExpanded={false}
+        onToggleExpanded={vi.fn()}
+        laneCount={0}
+        isLaneOpen={false}
+        onToggleLanes={vi.fn()}
+        hidden={false}
+        onToggleHidden={vi.fn()}
+        isSoloed={false}
+        isHalfLitSolo={false}
+        onToggleSolo={vi.fn()}
+        onFxChainChange={vi.fn()}
+        onOpenFxRack={vi.fn()}
+        columnWidth={220}
+        theme={defaultTimelineTheme}
+        {...overrides}
+      />,
+    );
+  });
+  return host;
+}
+
+/** The structural disclosure — the caret, not the `∿` lane toggle. */
+function caret(host: HTMLElement): HTMLButtonElement {
+  const el = Array.from(host.querySelectorAll("button")).find((b) =>
+    b.getAttribute("aria-label")?.includes("tracks"),
+  );
+  if (!el) throw new Error("no disclosure caret");
+  return el as HTMLButtonElement;
+}
+
+afterEach(() => {
+  document.body.innerHTML = "";
+});
+
+describe("TimelineGroupHeader disclosure caret", () => {
+  // Guards a regression that shipped once: the caret silently reverted to a
+  // smaller, non-mono, rotated glyph unlike the property panel's carets.
+  it("swaps the glyph rather than rotating one", () => {
+    expect(caret(renderHeader({ isExpanded: false })).textContent).toContain("▸");
+    expect(caret(renderHeader({ isExpanded: true })).textContent).toContain("▾");
+  });
+
+  it("does not rotate the glyph", () => {
+    const glyph = caret(renderHeader({ isExpanded: true })).querySelector("span");
+    expect(glyph?.getAttribute("style") ?? "").not.toContain("rotate");
+  });
+
+  it("keeps the caret mono at 13px, not back down at the 11px the row inherits", () => {
+    // Only this component's own className — the panel carets are not read here,
+    // and this does not claim to pin a match against them.
+    const className = caret(renderHeader()).className;
+    expect(className).toContain("font-mono");
+    expect(className).toContain("text-[13px]");
+    expect(className).not.toContain("text-[11px]");
+  });
+});
diff --git a/packages/studio/src/player/components/TimelineGroupHeader.tsx b/packages/studio/src/player/components/TimelineGroupHeader.tsx
index c579bc28f..b28994b31 100644
--- a/packages/studio/src/player/components/TimelineGroupHeader.tsx
+++ b/packages/studio/src/player/components/TimelineGroupHeader.tsx
@@ -77,7 +77,11 @@ export function TimelineGroupHeader({
         aria-expanded={isExpanded}
         aria-label={`${isExpanded ? "Hide" : "Show"} ${label} tracks`}
         title={`${isExpanded ? "Hide" : "Show"} tracks`}
-        className={`flex h-6 w-6 shrink-0 items-center justify-center rounded border-0 bg-transparent p-0 text-[11px] focus-visible:outline focus-visible:outline-1 focus-visible:outline-[#3CE6AC] ${
+        // Mono, like both of the property panel's disclosure carets. The size is
+        // this row's own call and not a match to either of them: the node-body
+        // caret sits under `text-[9px]`, and `hf-fx-preset-run-caret` has no
+        // size rule at all, so there is no measured target to match.
+        className={`flex h-6 w-6 shrink-0 items-center justify-center rounded border-0 bg-transparent p-0 font-mono text-[13px] focus-visible:outline focus-visible:outline-1 focus-visible:outline-[#3CE6AC] ${
           isExpanded ? "text-white" : "text-white/55 hover:text-white"
         }`}
         onPointerDown={(event) => event.stopPropagation()}
@@ -86,9 +90,9 @@ export function TimelineGroupHeader({
           onToggleExpanded();
         }}
       >
-        <span aria-hidden="true" style={{ transform: isExpanded ? "rotate(90deg)" : undefined }}>
-          ▸
-        </span>
+        {/* Swapped, not rotated: both panel carets swap, and a rotated ▸ sits
+            off-centre in its box because the glyph is not square. */}
+        <span aria-hidden="true">{isExpanded ? "▾" : "▸"}</span>
       </button>
       <span aria-hidden="true" className="shrink-0 text-[12px] leading-none text-white/50">
         ▤